Alignment layer for liquid crystals

Details Alignment layer for liquid crystals Alignment layer for liquid crystals

1995-10-18

1998-04-28

Dean, Ralph H.

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

With charge transferring layer of specified composition

349123, G02F 11337

Patent

active

057442037

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to an alignment layer, an alignment layer, comprising a specific polymer compound, which has a high alignment ability for liquid crystals.


BACKGROUND OF THE INVENTION

A liquid crystal display device is an electrooptical device comprising a liquid crystal material whose optical characteristics vary according to an external electrical field. For example, in a TN (twisted nematic) type liquid crystal display device, a liquid crystal alignment layer is provided on the surface of a solid substrate so that a liquid crystal molecule on the surface of the substrate is in a uniform alignment state to the surface, and the surface is subjected to a rubbing treatment. That is, a liquid crystal alignment layer obtained by preparing a thin film of a heat-resistant polymer such as a polyimide and a polyamide on a solid substrate such as a glass plate by means of a spin-coating, printing or dipping method or the like, drying or curing the thin film thus prepared, and then rubbing the thin film in one direction by means of a cloth or the like. Thus, a liquid crystal molecule is aligned in one direction by the resulting liquid crystal alignment layer and, at the same time, a liquid crystal alignment tilt angle (a pretilt angle) which is generally about 2 to 4 degree to the surface of the substrate is obtained.
Further, a display device with super twisted birefringence effects (STN) which is excellent in display contents has been developed for a large-sized display (T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (10), 1021 (1984)). For obtaining the super twisted birefringence effects, a nematic liquid crystal blended with a chiral agent as an optically active material is used. In such a display device, a liquid crystal molecule twists from 180 to 270 degree in a liquid crystal display device as compared with a TN type device which twists at about 90 degree, and the larger the twist angle, the better the dependence upon viewing angles. A large pretilt angle of liquid crystal is required in order to produce a large twist angle. More specifically, a pretilt angle of at least 5 degree is required for obtaining a twist angle of 240 to 270 degree.
Conventionally, as a means of enlarging pretilt angle of a liquid crystal molecule, a method for forming an oblique vaporation layer of silicon oxide or the like and a method for forming a film of an organic polymer having a long chain (Japanese Patent Publication (Kokai) Nos. 177514/89 and 297819/87) and subjecting the film to a rubbing treatment have been known. However, these conventional methods have disadvantages in that the cost for mass production becomes high since oblique vaporation of silicon oxide or the like is carried out in a vacuum system and production ability of these methods is poor due to a batch process.
In the case of using a layer of the above-described long chain polyimide, the pretilt angle tends to vary depending upon the type of the rubbing treatment method and the heating temperature, and, therefore, it was technically difficult to produce stably the desired pretilt angle. Further, the layer of the long chain polyimide generally has problems in that, since it has poor adhesion to the glass substrate, the coated film of polyimide tends to be partially peeled off during the rubbing treatment thereby causing poor alignment such as generation of disclinations.
A method for improving adhesion of the coating layer to the glass substrate by using a diaminosilane represented by the general formula (I): ##STR1## wherein R.sub.1 represents a divalent hydrocarbon group, R.sub.2 and R.sub.3 each represents a monovalent hydrocarbon group and n is an integer of from 1 to 4, as a diamine component used in synthesizing a polyimide or a polyamide, as proposed in Japanese Patent Publications (Kokai) No. 135919/82 and No. 72924/83. However, this method does not generate a satisfactory high pretilt angle.
Furthermore, Japanese Patent Publication (Kokai) No. 62616/89 discloses that a polyamide containing a siloxane component i

REFERENCES:
patent: 5008361 (1991-04-01), Lee

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